There is a lot of emphasis on joy in Apostle Paul's letter to Philippians. "Always offering prayer with joy in every prayer I pray for you." (Phil 1:4) "Rejoice in the Lord always, and again I say unto you, rejoice." (Phil 4:4)
Philippians was written when Paul was in prison (Phil. 1:13). It is challenging to see that Paul wrote so much about joy while he was in a prison. It's one thing to preach about joy when all our circumstances are comfortable. It's quite another thing to write about it when our circumstances are difficult. Paul's words here teach us that it is possible for a Christian to have joy under all circumstances. That is the mind of Christ, the attitude of Christ.
Jesus spoke most about joy on the night He was crucified (in John 15 and 16). At the last supper, He told His disciples, "These things have I spoken unto you that your joy may be full." "No man can take away your joy." "I want to give you My joy." He was going to be falsely accused and crucified publicly as if He were a criminal in a few hours from then. Yet He was going around sharing His joy with others and encouraging them.
This is the mind and attitude of Christ that Paul had. He was full of joy in prison. We don't know whether Paul was only under house arrest as a prisoner at the time he wrote this letter (Acts 28:16, 30,31) or whether he was in an actual Roman prison. The Roman prisons of those days were dark dungeons full of rats, mosquitoes and creeping insects, where prisoners had to sleep on the floor and were given very little food. Whichever of these two locations Paul may have been in, the circumstances were definitely not pleasant. Yet in such circumstances, Paul was full of joy He had been imprisoned for preaching the gospel. But he had no tears for his own sorrows. He didn't want any sympathy from anyone either. He was full of joy.
What an example Paul is for Christians who live in comfort and yet complain at the smallest inconvenience. How often we see believers trying to get sympathy from others just because they are facing a little difficulty or going through a small trial. Paul doesn't say a word here about his sufferings. He said, "I thank my God in all my remembrance of you, always offering prayer with joy in my every prayer for you all " (Phil 1:3,4) I can imagine him writing that after a whole night of being bitten by mosquitoes, trying to avoid the rats that were crawling around the dungeon floor, and the insects and things that were there. He wrote that probably after a whole night of being bitten by mosquitoes; and he may not have had much warm clothing to cover him either. His joy did not come from his circumstances, but from the grace of God that he saw in the believers a Philippi.
Many years earlier he had been led by the Lord through a vision, to go to Philippi (Acts 16: 9-12). He had followed that vision and gone there and led people to the Lord and been imprisoned in Philippi too. The jailer who was converted there was probably an elder in the church in Philippi now he would have told the people then, "I saw this man rejoicing there in prison." Paul's joy came out of a life that was spent usefully for the Lord. When you come to the end of your life, the thing that will bring you joy is the fact that in the days when God gave you health and strength you spent your life serving the Lord, gathering people for His kingdom and building His church. Think of it now, so that when you come to the end of your life like Paul you can thank God for what He did with your life.